The molecular details of the regulation of gene expression during fertilization, development and the activation of growth of sea urchin embryos will be examined. The role and extent of development regulation of transcription or post-transcriptional stability will be examined by analysis of the sequences present in mRNA and hnRNA populations at various stages of sea urchin development. Using both single-copy DNA and repetitive DNA tracers as hybridization probes, the sequence complexity and various abundancy classes of nuclear RNA from both repetitive and unique sequences will be determined in order to establish the extent transcription is regulated during development. Single-copy sequences purified for mRNA sequences present at a specific stage and cDNA probes produced by reverse transcriptase from poly(A) mRNA of a specific stage will be reacted to hnRNA preparations of the same and different stages to determine the presence, absence or concentration of such sequences in hnRNA of stages when they appear in mRNA and when they do not appear in mRNA. The translational regulation of the activity of maternal mRNA will be examined. The complex changes in the poly(A) which is associated with the maternal mRNA will be analyzed further to relate these changes with the changes in activity of the mRNA. cDNA probes of the sequences in maternal mRNA will be used to determine the percent of the sequences which move onto the polysomes when activation of protein synthesis occurs and to measure deactivation and decay of the mRNA. The regulation of growth and ribosomal RNA synthesis during sea urchin development will be further investigated using cl ned ribosomal DNA from the sea urchin as a hybridization probe to identify precursor. The rates of transcription of the ribosomal genes will be measured during cleavage where accumulation of radioactive 28 and 18S RNA is difficult to detect and in feeding plutei where 28S and 18S rRNA accumulates at 15 times the rate it accumulates in unfed plutei.